Condenser microphone pattern adjustment

ABSTRACT

A condenser microphone with at least two microphone capsules, each including a diaphragm and a backplate. The backplates of both the first capsule and second capsule having an electret bias. The first capsule having a first polar pattern, and the second capsule having a second polar pattern. The second capsule having an external voltage bias that is continuously variable over a certain voltage range. This external voltage bias can be applied to the second diaphragm or second backplate. The microphone&#39;s total polar pattern consists of a combination of the first polar pattern and the second polar pattern. Using the external voltage bias of the second capsule, the microphone&#39;s total polar pattern is continuously variable throughout a range set by the external voltage bias.

FIELD

The disclosure relates to a condenser microphone of which the polarpattern can be adjusted using the superposition of both electret andexternal biasing.

BACKGROUND

Microphones convert sound into an electrical signal through the use of atransducer that includes a diaphragm to convert sound into mechanicalmotion, which in turn is converted to an electrical signal. Microphonescome in several types, including condenser, dynamic, ribbon, carbon, andlaser. Condenser microphones, also known as capacitor microphones orelectrostatic microphones, are among the more common. A condensermicrophone, at the most basic level, is a capacitor with a thin platethat functions as a diaphragm and thicker backplate. A voltage orelectric potential difference is created between the diaphragm andbackplate. Often, this is done by the backplate receiving a fixed chargeor voltage. Air pressure from sound waves striking the diaphragm causesthe diaphragm to vibrate, which changes the distance between the twoplates, causing a change in the capacitance of the microphone. Thedynamic change in capacitance is reflected in a dynamic change ofvoltage across the capacitor, which is taken as the signal that istransmitted to an amplifying stage.

In most condenser microphones, the voltage bias of the backplate iscreated through two methods. The first method is through an externalvoltage source, which allows the adjustment of the voltage bias byadjusting the voltage provided by the external voltage source. Thesecond method to create a voltage bias is using an electret material forthe backplate. Electret materials are able to hold static electricalcharge for long periods of time without an external supply. Biasing amicrophone with an electret material has the benefit of not requiring anexternal power source, so it lends itself to handheld or wireless uses.However, electret biasing cannot be adjusted like external biasing can.

A major characteristic of microphones that influences microphone designis the microphone's polar pattern. This pattern defines a microphone'sdirectionality, the sensitivity of a microphone to sounds arriving fromdifferent angles to the microphone's central axis. For example, anomnidirectional microphone is equally sensitive to sounds received fromall directions. These microphones are often used in studio and othervenues with good acoustics. A microphone with a cardioid polar pattern,so-called because the pattern resembles a heart, is sensitive to soundsreceived from the front of the microphone but is less sensitive orblocks sound received from the sides or back of the microphone. Thesemicrophones are often used when recording a singer during a liveperformance.

Other polar patterns include super-cardioid and hyper-cardioid, whichare variations of a cardioid pattern and that have a more focusedsensitivity to the sound received from the front of the microphone. Butmicrophones with these patterns do not block sound received from behindthe microphone as well as a cardioid microphone. Finally, abi-directional microphone is equally sensitive to sound received alongone axis, but sound received along the perpendicular axis is blockedout. Common polar patterns are illustrated in FIG. 1.

The various polarization patterns can also be described as a combinationof the omnidirectional and bi-directional polar patterns.Mathematically, this is illustrated by the equation 1=A+B cos θ, whichhas been normalized to 1. A is the omnidirectional portion of thepattern and B is the bi-directional portion. If one were to add equalproportions of the omnidirectional portion and bi-directionalportion—i.e., 0.5+0.5 cos θ—the microphone would have a cardioid polarpattern. Table 1 shows how one could produce the common polar patternsusing a dual diaphragm microphone that has both an omnidirectionalportion and a bi-directional portion.

TABLE 1 Pattern Equation (A + Bcos θ) Omnidirectional 1 Sub-cardioid0.7 + 0.3cos θ Cardioid 0.5 + 0.5cos θ Super-cardioid 0.37 + 0.63cos θHyper-cardioid 0.25 + 0.75cos θ Bi-directional cos θ

As mentioned, certain polar patterns are better suited for certainenvironments or uses (e.g., studio recording versus live recording). Buthaving a different microphone for every situation can become cumbersome,so manufactures design microphones that have the ability to changebetween different polar patterns. One way to build a microphone withthis ability is to include multiple microphone capsules, each containinga diaphragm and backplate tuned to a specific polar pattern. The outputsof these different capsules are then added to or subtracted from eachother to form new polar patterns.

For example, a condenser microphone may include two capsules, eachincluding a diaphragm and a backplate. One capsule may have anomnidirectional polar pattern while the other capsule may have abi-directional polar pattern. By adjusting the amount of each signalthat is included in the final microphone output, the microphone mayexhibit multiple different polar patterns. One way to do this would beto utilize external biasing on one or both capsules. The sensitivity ofeach capsule is proportional to its bias voltage. By adjusting theexternal biasing, one would be able to adjust the sensitivity orstrength of the capsules, and thus, each capsule's contribution to themicrophone's total output.

However, in real world applications, microphones are often limited toonly a few options. As an example, a dual diaphragm condenser microphonemay include two diaphragms with a common backplate in which both sideshave a cardioid polar pattern. If the two back-to-back cardioids areadded together, the microphone would have an omnidirectional polarpattern: (0.5+0.5 cos θ)+(0.5−0.5 cos θ)=1. The difference in sign onthe B value is attributable to the front facing cardioid pattern, ifassigned a positive polarity, having the opposed polarity of the backfacing cardioid pattern, which faces the opposed direction. When thecardioids are subtracted from each other, the microphone would have abi-directional polar pattern: (0.5+0.5 cos θ)−(0.5−0.5 cos θ)=cos θ.Further, subtracting only half as much of the rear cardioid creates amicrophone with a hyper-cardioid pattern: (0.5+0.5 cos θ)−0.5(0.5−0.5cos θ)=0.25+0.75 cos θ. These simple adjustments are often done with aswitch on the microphone.

In another example, a dual diaphragm condenser microphone may includetwo microphone capsules, one in front of the other, where each capsuleincludes a diaphragm and a backplate. The front capsule is tuned to apoint half-way between cardioid and super-cardioid. When the rearcapsule, which has a cardioid pattern, has the same polarity as thefront capsule, the microphone's pattern is cardioid. When the rearcapsule is switched to have the opposite polarity as the front capsule,the microphone's pattern is super-cardioid. This technique can beimplemented such that each pattern of the microphone's total output tohave similar sensitivities. This technique can be done with otherpatterns. For example, the front capsule is tuned between hyper-cardioidand sub-cardioid, and the back capsule is used to switch between the twopatterns based on its sensitivity and polarity in relationship with thefront capsule.

However, as can be seen, microphones that allow switching betweendifferent polar patterns only allow the selection of a discrete numberof patterns, especially if their backplate is using electret biasing.Further, although external biasing may allow a wider variety of patternsfor a microphone, this biasing method usually limits the mobility of themicrophone and is generally unworkable for smaller, wirelessmicrophones.

SUMMARY

The following presents a simplified summary of the disclosure in orderto provide a basic understanding of some aspects of the disclosure. Thissummary is not an extensive overview of the disclosure. It is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. The following summary merelypresents some concepts of the disclosure in a simplified form as aprelude to the more detailed description provided below.

Aspects of this disclosure relate to a condenser microphone with twomicrophone capsules, each including a diaphragm and a backplate. Thediaphragms separately receive sound and convert it to electricalsignals. Each microphone capsule has its own polar pattern, whichrepresents the sensitivity of the microphone capsule to sound receivedfrom different angles. Through the use of superposition, the outputs ofthe two microphone capsules are combined to a single microphone outputthat has a single polar pattern.

With another aspect of this disclosure, each diaphragm and correspondingbackplate microphone may be biased by two different methods. The firstmethod is by biasing a backplate with an electret material or similarbiasing type material. This method includes using an electret materialas a backplate, and thus biasing is not variable after the microphonehas been built. The second method is by providing an external biasvoltage. This may be done by applying a voltage to a diaphragm. Thismethod of biasing is adjustable, so one can adjust the level of biasingafter the microphone has been built, and in this way, adjust the polarpattern of the microphone.

With another aspect of this disclosure, both electret and externalbiasing may be used simultaneously on a microphone. This allows for themicrophone's polar pattern to be adjusted with a high degree ofcontinuous variability. Similarly, this can also be used to adjust themicrophone's sensitivity.

With another aspect of this disclosure, the adjustment of themicrophone's polar pattern may be done by dials or switches on themicrophone itself. Alternatively, these adjustments may be done remotelythrough wireless technology.

With another aspect of this disclosure, the external bias voltage may beapplied to any combination of microphone capsules in any number ofmechanical configurations. For example, in a dual diaphragm microphone,there are multiple configurations, including: (1) a front diaphragm anda front backplate followed by a back diaphragm and a rear backplate, inthat order; (2) two diaphragms on the outside with two backplates in themiddle; and (3) two diaphragms on the outside and a shared backplate inthe middle. Alternatively, the first capsule and the second capsule maybe aligned in the housing so that the capsules are on perpendicularaxes.

With another aspect of this disclosure, the combination of electret andexternal biasing allow for a microphone with continuous variability thatis also low power. This is useful in high-tier wireless handledmicrophones.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure and theadvantages thereof may be acquired by referring to the followingdescription in consideration of the accompanying drawings, in which likereference numbers indicate like features, and wherein:

FIG. 1 shows diagrams of common microphone polar patterns;

FIG. 2 shows an exploded view of an example condenser microphone;

FIG. 3 shows a diagram of three different orientations of diaphragms andbackplates in a dual diaphragm condenser microphone;

FIG. 4 shows a schematic of an example external biasing circuit for acondenser microphone;

FIG. 5A illustrates a polar plot of the example condenser microphone ofFIG. 2 with a 0 V external bias applied to the rear diaphragm;

FIG. 5B illustrates a polar plot of the example condenser microphone ofFIG. 2 with a −38 V external bias applied to the rear diaphragm;

FIG. 5C illustrates a polar plot of the example condenser microphone ofFIG. 2 with a −76 V external bias applied to the rear diaphragm;

FIG. 5D illustrates a polar plot of the example condenser microphone ofFIG. 2 with a −110 V external bias applied to the rear diaphragm;

FIG. 6A illustrates a frequency response plot of the example condensermicrophone of FIG. 2 with a 0 V external bias applied to the reardiaphragm;

FIG. 6B illustrates a frequency response plot of the example condensermicrophone of FIG. 2 with a −38 V external bias applied to the reardiaphragm;

FIG. 6C illustrates a frequency response plot of the example condensermicrophone of FIG. 2 with a −76 V external bias applied to the reardiaphragm; and

FIG. 6D illustrates a frequency response plot of the example condensermicrophone of FIG. 2 with a −110 V external bias applied to the reardiaphragm.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings, which form a part hereof, and in which is shown by way ofillustration various examples in which aspects may be practiced.References to “embodiment,” “example,” and the like indicate that theembodiment(s) or example(s) of the invention so described may includeparticular features, structures, or characteristics, but not everyembodiment or example necessarily includes the particular features,structures, or characteristics. It is contemplated that certainembodiments or examples may have some, all, or none of the featuresdescribed for other examples. And it is to be understood that otherembodiments and examples may be utilized and structural and functionalmodifications may be made without departing from the scope of thepresent disclosure, including adjusting the electrical component values.

Unless otherwise specified, the use of the serial adjectives, such as,“first,” “second,” “third,” and the like that are used to describeelements, are used only to indicate different elements that can besimilar. But the use of such serial adjectives are not intended to implythat the elements must be provided in given order, either temporally,spatially, in ranking, or in any other way.

Also, the terms “front,” “rear,” “back,” “side,” “parallel,”“perpendicular,” and the like, as well as descriptions in relation toaxes, may be used in this specification to describe various examplefeatures and elements. But these terms are used herein as a matter ofconvenience, for example, based on the example orientations shown in thefigures and/or the orientations in typical use. Nothing in thisspecification should be construed as requiring a specific threedimensional or spatial orientation of structures in order to fall withinthe scope of the claims.

FIG. 2 shows an exploded view of example microphone 100. Capsule housing101 contains the various components of the microphone and includesopenings that allow sound to reach those components. Side screen 103protects the components of microphone 100 from debris and moisture fromthe side. Similarly, screen 105 protects the components of themicrophone from debris and moisture from the front. Under screen 105 isgrill 107. Grill 107 can be made of metal, such as brass, steel, oriron. Grill 107 has a number of different functions, including providingprotection from physical damage and additional protection from debrisand moisture. Grill 107 also acts as a windscreen, which helps dissipategusts of air that would overload the microphone's diaphragm. This helpsreduce popping or plosiveness in the microphone signal.

Front diaphragm 113 rests within insulating frame 109. Insulating frame109 separates the various internal conductive components for microphone100 from the outer components, such as capsule housing 101 and grill107. Resting in between front diaphragm 113 and insulating frame 109 isfront diaphragm electrical contact 111. Separating front diaphragm 113and front backplate 117 is insulating spacer 115. Front backplateelectrical contact 119 rests in insulating spacer 121. Insulating spacer121 interacts with insulating frame 109 to contain the variouscomponents of the front capsule.

Front diaphragm electrical contact 111 and front backplate electricalcontact 119 allow the monitoring of the electrical signals of frontdiaphragm 113 and front backplate 117, respectively. These electricalsignals will change as sound interacts with front diaphragm 113,changing the capacitance between front diaphragm 113 and front backplate117. In this example, electrical signal representing received audiosignal is taken from front backplate 117. Front diaphragm electricalcontact 111 and front backplate electrical contact 119 also allow anyexternal bias to be applied to either front diaphragm 113 and frontbackplate 117, respectively.

Acoustic resistance element 123 acoustically isolates the front capsulefrom the rear capsule, which includes rear diaphragm 127 and rearbackplate 131. This is placed between insulating spacer 121 and reardiaphragm electrical contact 125. Rear diaphragm 127 is separated fromrear backplate 131 by insulating spacer 129. Rear diaphragm electricalcontact 125 and rear backplate electrical contact 133 allow themonitoring of the electrical signals of rear diaphragm 127 and rearbackplate 131, respectively. These electrical signals will change assound interacts with rear diaphragm 127, changing the capacitancebetween rear diaphragm 127 and rear backplate 131. In this example,electrical signal representing received audio signal is taken from rearfront backplate 131. Rear diaphragm electrical contact 125 and rearbackplate electrical contact 133 also allow any external bias to beapplied to either rear diaphragm 127 and rear backplate 131,respectively.

Plastic frame 135 interacts with acoustic resistance element 123 tocontain the components of the rear capsule. Plastic frame 135 hasvarious grooves that interact with plastic contact guide 137 to organizeand allow the various electrical connections to pass through to thecircuitry of the microphone. Plastic contact guide 137 rests on rubbercushion 139, which rests on plastic washer 141. Internal retaining ring143 and external regaining ring 145 function together to secure thevarious components of microphone 100 during use.

In microphone 100, the front capsule, which includes front diaphragm 113and front backplate 117, is tuned between two common polar patterns; inthis example, those patterns are hyper-cardioid and sub-cardioid. Alsoin this example, front backplate 117 has an electret bias of −100 V.Because this backplate is biased with an electret material or a similarbiasing type material, it cannot be adjusted.

In microphone 100, the rear capsule, which includes rear diaphragm 127and rear backplate 131, is tuned to a standard cardioid pattern. In thisexample, the rear capsule has a variable bias. This variability allowsmicrophone 100 to have a continuously variable polar pattern anywherebetween the two polar patterns of the front capsule, which in thisexample is hyper-cardioid and sub-cardioid patterns. To achieve thiscontinuous variability, one could vary the voltage bias of the rearbackplate 131 between −55 V and +55 V, but varying above and below 0 Vcan create issues with the switching polarity. Rather, an easier methodwould be to apply the same range of voltage but only at positive ornegative voltages, such as 0 V to +110 V or 0 V to −110 V. Usingsuperposition, the goal of biasing the rear capsule between −55 V and+55 V can be achieved by applying an electret bias of −55 V to rearbackplate 131 and applying a variable external voltage of 0 V to −110 Vto rear diaphragm 131. Alternatively, a variable external voltage of 0 Vto +110 V could be applied to rear backplate 131.

Microphone 100 is configured so that the diaphragm and backplates areoriented the same direction. However, this is not necessary. Forinstance, the rear capsule could be flipped so that the two backplatesare together. Alternatively, the two diaphragms could share a singlebackplate. Diagrammed, these three variations are found in FIG. 3.

The chosen mechanical arrangement influences how each capsule's polarpattern is combined with the other capsule's polar pattern to producethe final microphone output. The mechanical arrangement also affects howbiasing is applied to each capsule. External bias voltages may beapplied to any combination of diaphragms or backplates. Electret biasingcan be applied to either side of a back plate, or both sides in the caseof a shared backplate. Electrical signals can also be taken from anycombination of diaphragms or backplates. However, one must be mindful ofhow the orientation of the two capsules affects the polarity when addingtogether the outputs from each capsule. For example, flipping the rearcapsule so that the two backplates are near each other (i.e., the middlearrangement above) also flips the polarity when adding the rearcapsule's output to the front capsule.

FIG. 4 shows an example of a schematic for circuit 200 that applies theexternal bias voltage to rear diaphragm 127 in microphone 100 of FIG. 2.Circuit 200 is connected to external biasing reference voltage 201 whichis connected to a DC voltage gain regulator 203. Using DC voltage gainregulator 203, various voltages can be applied to bias the reardiaphragm 127, which is connected to circuit 200 at resistor 243, asindicated. In this example, DC voltage gain regulator 203 allows avoltage range of 0 V to 5 V. Control of DC voltage gain regulator 203can be physical (e.g., with a dial or knob on the microphone) or througha wireless remote.

Circuit 200 is designed as a closed loop circuit to allow feedback tocontrol for temperature, lot-to-lot differences, aging, and othervariations. In this example, circuit 200 is in an inverting gainconfiguration. This means that the input voltage is applied to theinverting input terminal of op-amp 215, making the output signal fromop-amp 215 the opposite polarity or 180 degrees out of phase with theinput signal.

On the input side, a low pass filter, consisting of resistor 205 andcapacitor 207, is included to provide a stable input signal to theinverting input terminal of op-amp 215, especially since the inputvoltage will change throughout operation as a user adjusts the externalvoltage bias in order to adjust the polar pattern of the microphone.Input resistor 209 separates the input signal from the feedback signaland creates a virtual earth summing point. Resistors 211 and 213 arefeedback resistors with values chosen in relation to input resister 209and in view of the goal gain of circuit 200. In this example, tworesistors were used rather than one large resistor due to real worldconstraints of resistors, which are limited by the maximum voltage thatcan safely be applied to a single resistor. Capacitors 217 and 219function as low pass filters to increase performance by providing morestability in the system.

In this example, the non-inverting terminal of op-amp 215 is connectedto ground, making ground the common mode voltage of op-amp 215 inputs.Connecting the non-inverting terminal to ground was done in this exampleto simplify the circuit design because ground provides an easy referencepoint. However, not all op-amps necessarily have the capability to havetheir common mode voltage be at ground. In that case, one would have anon-ground reference that could vary the common mode voltage duringoperation, creating additional complexity in the circuit design toaccount for the this.

The output of op-amp 215 is connected photocouplers 219, 221, and 223.Photocouplers transfer electrical signals using light. The components ofa photocoupler include a light emitting diode at the input and a chainof photodiodes at the output. In one construction, a photocoupler, suchas Toshiba's TLP3924, includes an infrared emitting diode that isoptically coupled to a series connected photodiode array. In FIG. 4, the“A” indicates the anode and “K” indicates the cathode of the diode onthe input side. On the diode of the output side, O+ indicates the anodeand O-indicates the cathode.

In FIG. 4, photocouplers 219, 221, and 223 are connected in a string tocreate the large bias voltage appropriate for biasing condensermicrophones. The choice of photocoupler depends on the biasing goal. Inthis example, the photocouplers 219, 221, and 223 can each maintain anoutput voltage of above 30 V with a much smaller input, such as ˜1.2 Vand −2 mA at each photocoupler. Resistor 225 is an input resistor thatlimits the maximum current to protect the photocouplers. Using thesephotocouplers or similar devices that can maintain a large outputvoltage with a small input provides the capability of having a low powercondenser microphone with a highly adjustable polar pattern. Onepotential use for this low power method of biasing condenser microphoneswould be in wireless and wired handheld microphones.

As illustrated in FIG. 4, the outputs of photocoupler 219, 221, and 223are connected to rear diaphragm 127 of microphone 100 through resistors241 and 243. The values of these resistors are large in order minimizethe amount of current that flows to rear diaphragm 127, creating a DChigh-impedance node. Capacitors 245 and 247 are included to ground anyAC signals before they reach rear diaphragm 127. Resistors 241 and 243along with capacitors 245 and 247 effectively provide a two-stagehigh-impedance low pass filter.

Circuit 200 also includes a pulldown circuit attached to the inputs andoutputs of photocouplers 219, 221, and 223. This pulldown circuit allowsphotocouplers 219, 221, and 223 to charge and discharge at similarrates. When applying voltage, photocouplers can quickly build up therequired bias voltage. However, when the voltage is removed, thephotocouplers will eventually discharge the bias voltage, but it takestime, discharging through the feedback resistors if the pulldown circuitwas not present. The pulldown circuit makes this discharge quicker byproviding a path to ground. In this example, the pulldown circuitcomprises transistors 237 and 239 and resistors 227, 229, 231, 233, and235.

Circuit 200 in FIG. 4 was designed to provide a continuously adjustableexternal voltage bias to rear diaphragm 127 of microphone 100 with arange of −110 V to 0 V. The resistor and capacitor values of thisexample are found in Table 2.

TABLE 2 Resistor Value (Ω) Resistor Value (Ω) Capacitor Value (F) 205 2M 229 100 k 207 2.2 n 209 2.5M  231 500 k 217 2.2 n 211 50M 233 500 k219 2.2 n 213 50M 235  1M 245 2.2 n 225 200 241 50M 247 4.7 n 227 500 k243 50M

FIGS. 5A-5D illustrate polar plots of microphone 100 at various externalbias levels, showing the variability of the pattern of the microphonethroughout the external biasing voltage range. For example, FIG. 5Ashows the polar plot with an external bias of 0 V, which makes rearbackplate 131 have a bias of −55 V, or the amount of its electretbiasing. This biasing gives the microphone a hyper-cardioid pattern. Bychanging the external bias to −38 V, rear backplate 131 has a bias of−17 V, or −55 V subtracting −38 V. This biasing gives the microphone asuper-cardioid pattern, as shown in FIG. 5B. As illustrated, thesuper-cardioid pattern is less receptive to sound from behind themicrophone and receptive to sound from a wider angle in front of themicrophone.

FIG. 5C shows a polar plot with an external bias of −76 V, which makesrear backplate 131 have a bias of 17 V. This biasing gives themicrophone a cardioid pattern, which has little sensitivity to soundfrom behind the microphone. By changing the external bias to −110 V, therear backplate 131 has a bias of 55 V. This biasing gives the microphonea sub-cardioid pattern, as shown in FIG. 5D. Because the externalvoltage is continuously variable to any point in between 0 V to −110 V,these figures show just four options.

FIGS. 6A-6D illustrate frequency plots of microphone 100 at variousexternal bias levels, showing how receptive the microphone is throughoutthe voltage range and at various angles. For example, FIG. 6A shows thefrequency plot with an external bias of 0 V, giving the microphone ahyper-cardioid pattern as illustrated in FIG. 5A. Microphone 100 is mostreceptive to frequencies at 0° (solid line), which is in front of themicrophone. FIG. 6A shows that microphone 100 is second most receptiveto frequencies at 180° (dotted line), or directly behind the microphone.This is consistent with FIG. 5A, which shows a hyper-cardioid patternthat is most receptive to frequencies in front of and behind themicrophone. In contrast, at 90° (dashed line) and 125° (dot and dashline), FIG. 6A shows that microphone 100 is less receptive at this biasvoltage, which is again consistent with a hyper-cardioid pattern asillustrated in FIG. 5A.

FIG. 6B illustrates the frequency plot of microphone 100 with anexternal bias of −38 V, giving the microphone a super-cardioid patternas illustrated in FIG. 5B. This pattern is similar to the hyper-cardioidpattern shown in FIGS. 5A and 6A. As can be seen, microphone 100 isagain most receptive to frequencies at 0° (solid line), or in front ofthe microphone, but microphone 100 is far less receptive to sound beingreceived from behind the microphone at 125° (dot and dash line) or 180°(dotted line). Further, microphone 100 is much more receptive now tofrequencies at 90° (dashed line), consistent with a super cardioidpattern as illustrated in FIG. 5B.

FIG. 6C illustrates the frequency plot of microphone 100 with anexternal bias of −76 V, giving the microphone a cardioid pattern asillustrated in FIG. 5C. Of the previous patterns, this pattern is theleast receptive of sound from behind the microphone. As shown,microphone 100 is again most receptive to frequencies at 0° (solidline), but it also is much more receptive of sound received at 90°(dashed line) than in FIG. 6B. Here, microphone 100 is also not veryreceptive to sound received at either 125° (dot and dash line) or at180° (dotted line). This is consistent with the cardioid patternillustrated in FIG. 5C.

FIG. 6D illustrates the frequency plot of microphone 100 with anexternal bias of −110 V, giving the microphone a sub-cardioid pattern asillustrated in FIG. 5D. This pattern is closer to an omni-directionalpattern, picking up more sound from behind the microphone. As shown,microphone 100 is again most receptive to frequencies at 0° (solidline), but it is also relativity much more receptive at 90° (dashedline), 125° (dot and dash line), and 180° (dotted line) than thepatterns shown in FIGS. 6A-6C. This is also consistent with thesub-cardioid pattern illustrated in FIG. 5D.

In another embodiment, a microphone capsule comprising a diaphragm; abackplate with a first biasing mechanism, such as an electret material,that is fixed; and a second biasing mechanism, such as an externalvoltage, that is variable and interacts with the first biasing mechanismto adjust at least a sensitivity or a polarity of the microphonecapsule. The second biasing mechanism can be applied to the diaphragm orthe backplate of the microphone capsule and can be varied remotely.

Other embodiments may include more than two microphone capsules andaligning the capsules in various orientations to each other. Forexample, another embodiment may be a mid/side microphone. In thisembodiment, one microphone capsule is pointed to the front of themicrophone and is tuned to a cardioid polar pattern. A second microphonecapsule is pointed to the side, or 90 degrees from the front of themicrophone. This second microphone capsule is tuned to a bi-directionalpattern. If the “left” lobe of the bi-directional pattern is negativeand the “right” lobe of the bi-directional pattern is positive, addingthe output of the second microphone capsule to the output of the firstmicrophone capsule would result in a total microphone output of acardioid pattern directed to the right of the front of the microphone.Similarly, subtracting the output of the second microphone capsule fromthe output of the first microphone capsule would result in a totalmicrophone output of a cardioid pattern directed to the left of thefront of the microphone. The degree to which the total microphone outputis directed left or right of the front of the microphone depends on theamount of output of the second microphone capsule is added to orsubtracted from the output of the first microphone output. One can usethe combination biasing of an electret and external biasing for thesecond capsule to provide a continuously variable total microphoneoutput to any angle, right or left, from the front of the microphone.

Finally, although the subject matter has been described in languagespecific to structural features and/or methodological acts, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A microphone capsule comprising: a diaphragm; abackplate with a first biasing mechanism that is fixed; and a secondbiasing mechanism that is variable and interacts with the first biasingmechanism to adjust at least a sensitivity or a polarity of themicrophone capsule.
 2. The microphone capsule of claim 1, wherein thefirst biasing mechanism is an electret material.
 3. The microphonecapsule of claim 2, wherein the second biasing mechanism is an externalvoltage.
 4. The microphone capsule of claim 1, wherein the secondbiasing mechanism is applied to the diaphragm.
 5. The microphone capsuleof claim 1, wherein the second biasing mechanism is applied to thebackplate.
 6. The microphone capsule of claim 1, wherein the secondbiasing mechanism is continuously variable.
 7. The microphone capsule ofclaim 1, wherein the second biasing mechanism is able to be variedremotely.
 8. A method for biasing a microphone capsule comprising:applying a fixed bias to a backplate to create an electric potentialbetween the backplate and a diaphragm; and applying a variable bias thatinteracts with the fixed bias to adjust at least a sensitivity or apolarity of the microphone capsule.
 9. The method of claim 8, whereinthe fixed bias is created with an electret material.
 10. The method ofclaim 9, wherein the variable bias is applied by an external voltage.11. The method of claim 9, wherein the variable bias is applied to thediaphragm.
 12. The method of claim 9, wherein the variable bias isapplied to the backplate.
 13. The method of claim 10, wherein thevariable bias is continuously variable.
 14. The method of claim 10,wherein the variable bias is able to be adjusted remotely.
 15. Amicrophone comprising: at least a first microphone capsule with a firstpolar pattern and a second microphone capsule with a second polarpattern; the second microphone capsule comprising at least a diaphragmand a backplate, wherein the second capsule has both a fixed bias and avariable bias; wherein the variable bias allows the adjustment of atleast a sensitivity or a polarity of the second polar pattern; andwherein the first polar pattern and second polar pattern are combined toproduce a total microphone polar pattern that is variable based on thevariable bias of the second capsule.
 16. The microphone of claim 15,wherein the fixed bias is created by an electret material on thebackplate.
 17. The microphone of claim 16, wherein the variable bias iscreated by an external voltage.
 18. The microphone of claim 17, whereinthe variable bias is applied to the diaphragm.
 19. The microphone ofclaim 17, wherein the variable is applied to the backplate.
 20. Themicrophone of claim 17, wherein the microphone further comprises awireless device that allows the adjustment of the variable bias to bedone remotely.